The present invention relates to a method for removal of dissolved oxygen from organic liquids by use of a solid state catalyst. In doing so the dissolved oxygen is converted by the action of a reducing agent to water.
The presence of dissolved oxygen in organic liquids which are utilized in chemical processes in extremely large amounts of several metric tons per hour can lead to corrosion of equipment parts or to unwanted side reactions with other input materials. Because of the high throughputs, oxygen amounts in the ppm range are sufficient for that to occur. In most chemical processes high temperatures and pressures exist, enabling the occurrence of unwanted reactions between dissolved oxygen and other input materials.
The removal of dissolved oxygen from water is already known (K. Matt, Chemie-Technik, 20 (10), 44-45, 1991/A. Brehm, U. Antons, Reduction of Oxygen Dissolved in Water by Means of a Fluidized Bed Reactor, Chemie Ingenieur Technik 70 (1+2), 176-181, 1998). This action is utilized mainly to prevent the corrosion of piping runs and apparatus in water circuits.
A catalytic method for removal of oxygen from sea water which was utilized subsequently in subterranean oil reservoirs is described in WO 01/85622.
As a matter of principle in oxygen removal physical and chemical methods are to be differentiated. Among physical methods are thermal degassing, stripping, gas removal by means of evacuation or combinations of these methods. Physical methods are of course characterized by having high investment costs and considerable energy consumption for large throughputs. Nevertheless the remaining oxygen concentrations are still frequently too high.
On these grounds chemical methods for removal of oxygen from water are also utilized. Thus after addition of hydrazine oxygen reacts completely to produce water and nitrogen. However, hydrazine is poisonous, is strongly endangering to water, is corrosive and may be involved with unwanted side reactions with other materials. Additionally, chemical methods are known which make use of sodium sulfite or amines.
For chemical removal of oxygen from water catalytic methods using different catalysts in the presence of reducing agents such as hydrogen can also be employed (J.-S. Moon, K.-K. Park, S.-W. Yun, G. Seo, A study on the Application of a New Dissolved Oxygen Removal System Using Activated Carbon Fiber Cartridge Catalyst, Official Proceedings—International Water Conference 61, 186-204, 2000).
The state of the art of the removal of oxygen from organic liquids has not been described. Should one wish to remove dissolved oxygen from an organic liquid, it must be insured beforehand that as a result of the catalyst or the reducing agent no chemical reaction takes place with the organic liquid that leads to the formation of unwanted byproducts. This could dramatically interfere with the entire course of the production. On the other hand the organic liquid to be treated must not deactivate the catalyst that is being used, which can for example cause the formation of sediment. Furthermore if the solubility of oxygen is greater in the organic liquids than in water and consequently the amount to be removed is also significantly higher. For instance, oxygen dissolves about 10 times better in methanol than in water (J. Tokunaga, Solubilities of Oxygen Nitrogen and Carbon Dioxide in Aqueous Alcohol Solutions, J. Chem. Eng. Data 20, 1, 41-46, 1975, and K. Fischer, M. Wilkens, J. Chem. Thermodynamics, 33, 1285-1308, 2001). As a result, very active catalysts must be employed, which moreover in the preferred embodiment convert the oxygen to for example water without heat input at room or ambient temperature.
Aggravatingly, in the removal of oxygen from organic liquids, there is also the fact that in chemical processes these are not present as a pure substance, but mostly contain a small amount of other organic and/or inorganic substances, which likewise are not inert. In known purification methods according to the state of the art water on the other hand is mainly utilized in separate heating and cooling circuits without contact with other media.
When mixtures of several different substances are present in chemical plants the removal of dissolved oxygen from the organic liquids can be especially required, if the mixtures can give rise to unwanted side reactions with oxygen. For example, the dissolved oxygen in an organic liquid can upon contact with sulfur-containing compounds at higher temperature cause the oxidation of these compounds to bring about formation of elemental sulfur. This can have fatal consequences, if elementary sulfur is deposited as a solid and plugs equipment parts. By removal of dissolved oxygen, higher availability of the installations are achieved, which is of enormous economic interest. Additionally plant safety is also enhanced since operation with dangerous material is not a factor interfering with operation of the plant.
Moreover the input of dissolved oxygen into installations can lead to the formation of explosive mixtures with organic compounds, in case the oxygen that is brought in, for example through degassing becomes enriched in parts of the installation and comes into contact with organic compounds.
The object of the present invention is to provide a method for the catalytic removal of dissolved oxygen from organic liquids, so that the undesirable side reactions and safety-related dangerous plant conditions are avoided.
In order to remove dissolved oxygen as cost-effectively as possible, preferably the method should work at room or ambient temperature without thermal treatment. Additionally the dissolved oxygen should be almost completely removed from the organic liquid.